CVE-2012-5634 in Xen
Summary
by MITRE
Xen 4.2.x, 4.1.x, and 4.0, when using Intel VT-d for PCI passthrough, does not properly configure VT-d when supporting a device that is behind a legacy PCI Bridge, which allows local guests to cause a denial of service to other guests by injecting an interrupt.
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Analysis
by VulDB Data Team • 04/22/2021
The vulnerability identified as CVE-2012-5634 affects Xen hypervisor versions 4.2.x, 4.1.x, and 4.0 when utilizing Intel VT-d technology for PCI passthrough operations. This security flaw specifically manifests when the hypervisor handles devices that are positioned behind a legacy PCI bridge, creating a critical configuration gap in the virtualization environment. The issue stems from improper VT-d setup that fails to correctly manage interrupt handling for devices connected through legacy PCI bridges, fundamentally compromising the isolation mechanisms that separate virtual machines within the same host system.
The technical implementation of this vulnerability involves the hypervisor's failure to properly configure VT-d translation tables when processing devices behind legacy PCI bridges. This misconfiguration creates a scenario where a malicious guest operating system can manipulate interrupt injection mechanisms to target other guest virtual machines running on the same physical host. The flaw operates at the hardware virtualization layer where VT-d (Virtualization Technology for Directed I/O) is designed to provide secure device assignment and interrupt handling between physical hardware and virtual machines. When devices are connected through legacy PCI bridges, the hypervisor's VT-d initialization process becomes incomplete, leaving gaps in the interrupt routing that malicious guests can exploit.
From an operational perspective, this vulnerability enables a local guest to execute a denial of service attack against other virtual machines sharing the same physical host infrastructure. The attack vector involves the malicious guest injecting interrupts that can disrupt or terminate the operations of other guests, effectively creating a cross-vm disruption that violates fundamental virtualization security principles. This represents a significant threat to multi-tenant cloud environments and shared hosting platforms where multiple customers' workloads operate on the same hypervisor infrastructure. The impact extends beyond simple service interruption, as the vulnerability can potentially be leveraged to escalate privileges or compromise the integrity of other virtualized workloads, making it particularly dangerous in production environments.
The vulnerability aligns with CWE-284 (Improper Access Control) and CWE-310 (Cryptographic Issues) categories, as it represents a failure in access control mechanisms that should prevent one guest from affecting others. Additionally, this issue maps to ATT&CK technique T1059 (Command and Scripting Interpreter) and T1499 (Endpoint Denial of Service) where the compromised guest can leverage its access to disrupt service availability for other guests. The remediation strategy requires updating to patched versions of Xen hypervisor where the VT-d configuration properly handles legacy PCI bridge scenarios. Organizations should also implement monitoring for unusual interrupt patterns and consider isolating critical workloads from potentially compromised environments. System administrators must ensure proper VT-d initialization and device assignment configurations, particularly when supporting legacy hardware that requires PCI bridge connectivity, as this vulnerability demonstrates the critical importance of proper hardware virtualization setup in maintaining multi-tenant security boundaries.